The present invention relates to spatial compounding. In particular, the present invention relates to compounding component frames of data associated with different steering angles to reduce speckle.
One component frame of data is acquired by scanning along scan lines at one angle relative to a transducer. A second frame of data is acquired by scanning along scan lines at a different angle. Each of the frames of data represents a different but overlapping region of a patient due to the angle of the scan lines. The frames of data are compounded together and displayed as an image. A line artifact exists where the region of the display image transitions from areas associated with different numbers of component frames of data. A leftmost portion of the display image corresponds to a single component frame. A center, lateral or azimuth position near the transducer is associated with all of the component frames.
In order to avoid the line artifacts, the compounded information is filtered. For example, a low-pass filter is applied to data representing spatial locations on each side of the line artifact. Further minimization of the line artifact is provided by averaging, such as normalizing the combined data by the number of component frames associated with any spatial location. Data for each spatial location is preweighted with a weighting factor that is a function of the number of component frames used to represent that spatial location. However, the process of normalization and filtering or smoothing the transition between different numbers of frames is complex or computationally excessive. Since the preweights change as a function of the number and spatial orientation of the various component frames, the frame rate of the compounded images may be limited.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below include methods and systems for displaying an image formed from compounded frames of ultrasound data acquired with different steering angles. Each component frame is associated with the scan of the entire displayed region, but with one or more different steering angles. For example, one frame of data is associated with no steering angle (e.g. scan lines normal to the transducer). Other frames of data have scan lines with different steering angles or steering angles adjusted from the steering angles of a nominal format. For some types of scanning, a majority of scan lines for each component frame are pointed in one direction (linear) or the same relative direction with a common scanning apex (sector, curved-linear, or Vector(copyright)) scanning), and a minority of the scan lines are steered at different angles within each component frame to scan the rest of the display region. As a result, the benefits of spatial compounding component frames associated with different steering angles are provided without having to apply filtering to reduce line artifacts. For other types of scanning (e.g. curved-Vector(copyright)), each component frame of data has steering angles that change as a function of lateral position of the scan line. The scan lines of each component frame are at different angles than scan lines of another component frame of data. For example, one frame of data corresponds to a nominal scan line format, such as no steering or a specific steering pattern. Other frames of data have non-nominal scan line formats, such as one or more scan lines at adjusted or different steering angles.
The transmit and receive beamformers control the scanning format and the direction of the scan lines so that two or more frames represent the entire display area but different steering angles. A compound processor combines component frames for each spatial location within the display region. Each of the component frames for combining by the compound processor includes data representing the entire displayed region.
Further aspects and advantages of the invention are disclosed below in conjunction with the preferred embodiments.